I recently drained and refilled my CH system. After refilling and bleeding the
rads all was well until the following morning when one radiator remained cold.
There was no air in the top of the radiator and the pipes (microbore) were
warm, I drew some water, and I think some air, off through the drain cock and
the radiator heated up, however it has never heated up again without drawing
more water through.


The system is open vented, the feed and expansion tank is full and clean(ish)



Any ideas? Help much appriciated